In theory, creating a spare battery for the iPod or iPhone should be easy: connect a Dock Connector to a small battery pack and some status lights, put it all in a housing that matches Apple's devices, and ta-da -- you have a battery. But it's actually a lot more complicated than that. The iPhone in particular requires a reasonably robust battery for power, and making one that you can just pop onto an iPod or iPhone's body without screwing up its performance requires some skill.

Kensington has already released the Battery Pack and Charger for iPhone and iPod, a $70 repackaging of its earlier $60 Portable Power Pack for Mobile Devices with a Dock Connector cable, and now it has unveiled the Mini Battery Pack and Charger for iPhone and iPod ($50). Unlike these earlier products, which were rectangular bricks that could as easily be connected to any USB device as the iPod or iPhone, and basically dangled at a distance, the Mini Battery Pack is shaped somewhat like an iPod classic, only slightly thicker than the 80GB version, and designed to be used without the mess of an extra cable. You plug it in, and it adds 2.38” of height, four status lights, and only a little extra weight. A hard plastic cap is included to keep the Dock Connector safe when it’s not in use.

There’s little question that the larger version of the Battery Pack, and for that matter the earlier Portable Power Pack, are on paper better values for the dollar. They deliver twice the stated power of the Mini Battery Pack, which Kensington now describes as capable of adding 30 hours of music or 6 hours of video to a third-generation iPod nano. Those keeping track of battery numbers will see these numbers as a hint better than the actual battery performance of a factory fresh iPod nano, but markedly better than Apple’s stated performance for that battery. Our testing showed better than anticipated results: we connected the Mini Battery Pack to a completely discharged 160GB iPod classic, providing it with a worst case scenario for supplying power, and with our standard audio (50%), video brightness (50%) and files (iTunes Store videos, including The Incredibles), we were able to get 7 hours and 6 minutes of video playback time—a little better than the performance of the 6.75 video hour stock battery on an 80GB iPod classic. Though each Apple device will vary in performance, the fact that the Mini Battery Pack could keep a hard drive-based iPod playing video for this long is a good sign; it can outperform Kensington’s estimates by at least a little.

Several other factors weighed on our consideration of the Mini Battery Pack’s rating. First, despite its diminished capacity relative to the full-sized model, this version is substantially more convenient to carry and use. While we still like the concept of a backpack-style attachment for iPods and iPhones, such a design is increasingly inconvenient given the form factors and differing needs of these devices, so a bottom-mounting attachment generally makes sense. The exception is for the iPod nano and iPod touch, which have bottom-mounted headphone ports that are obscured by such an attachment; for these devices, the Battery Pack serves only as a recharger, rather than a battery to be used simultaneously with audio-out functionality.

On a related note, Mini’s practicality with the iPhone turned out to be better than we had expected. There is just enough of a gap between the battery and iPhone’s bottom to avoid interfering with audio to a significant extent: we were able to be heard without any echoing regardless of whether we were on speakerphone or standard iPhone handset mode, and only a tiny and inoffensive “end of sentence” echo could be heard on our caller’s end when our caller finished talking. This is a good thing in that the Mini Battery Pack can add 3 hours to the iPhone’s calling battery life, and can actually be used during calls without earphones and a separate mic.

More mixed were two other factors. We liked the simplicity of Mini’s indicators, with three blue lights to indicate the charge level and a fourth red and green alternating light to indicate charging or the nearly complete depletion of the charge. The lack of a button to trigger these lights may be an issue for some users, however; you’ll need to plug Mini in to see how much power remains. And then there’s its billing as a Mini Battery Pack and Charger. Unlike the more expensive versions, which actually come with a wall charger, this one includes only a retracting cable, which you’ll need to connect to your computer’s USB port.

Overall, the Mini Battery Pack and Charger is basically a less expensive and less well-appointed version of Kensington’s two earlier iPod- and iPhone-ready battery products, offering mixed virtues. Much like Apple’s iPod family, you get less if you pay less, but you also have less to carry around and worry about. For users who require additional battery power or the ability to power spare non-Apple devices, the full-sized Battery Pack and a recent rival, APC’s UPB10 are definitely better choices if you’re willing to pay the price difference to get them, but we think this model’s convenience and lower price make it an equally viable option. It’s a good battery, and worthy of our general recommendation.

Editors' Note: iLounge only reviews products in "final" form, but many companies now change their offerings - sometimes several times - after our reviews have been published.
This iLounge article provides more information on this practice, known as revving.